Abstract：The three-level hybrid active neutral point clamped (3L-HANPC) converter has emerged as a preferred power conversion interface in modern energy systems due to its inherent advantages, such as high efficiency, high power density, and moderate cost. However, the reliability of such converters remains a pressing concern, primarily due to their susceptibility to switching faults. Among various fault-tolerant schemes, configuring shared redundant units is considered a cost-effective solution for three-level converters. It is mainly designed for T-type converters, and the redundant fully controlled devices typically operate in a standby state under normal conditions, resulting in low utilization of these components. This paper proposes a novel fault-tolerant 3L-HANPC converter and operating method that leverages the functional reuse of fully controlled redundant devices. In the proposed scheme, redundant devices are not limited to backup roles; instead, they actively contribute to system operation even under normal conditions, significantly improving device utilization and overall cost-effectiveness of the system. During normal operation, the shared redundant fully controlled devices and the DC inductor form a half-bridge ripple suppression unit. It compensates for the main low-frequency harmonic component in the neutral-point current, thereby reducing voltage ripples across the DC split capacitor under high modulation index and low power factor conditions. Furthermore, to simplify the control of the half-bridge ripple suppression unit, the circuit is decoupled into an upper and a lower buck converter, which are designed to operate in discontinuous conduction mode. The corresponding duty cycle expressions are derived. Then, a DC ripple suppression control block diagram is developed, utilizing a single-voltage PI feedback loop. When open-circuit faults occur in switches, the fully controlled devices in shared redundant units dynamically transition to a fault-bridge-sharing mode, enabling the cross-phase multiplexing of redundant devices. To ensure safe cross-phase multiplexing of redundant devices, the voltage vector sequence is restructured, and the corresponding circuit operating modes under typical vectors are analyzed. Additionally, the feasible operating region is defined based on the duty ratios of the voltage vectors. Accordingly, the converter can tolerate multiple switch open-circuit faults in different bridge arms while maintaining the rated output voltage magnitude. The paper provides a detailed description of the proposed topology, including its structural composition, operating mechanisms in normal and fault conditions, and the associated control strategies. A 10 kW 3L-HANPC converter prototype was constructed to conduct ripple suppression under normal conditions and fault-tolerant operation under fault conditions. The experimental results verify the correctness and effectiveness of the proposed topology and control method. The following conclusions can be drawn. (1) Under normal conditions, the redundant devices effectively suppress the DC-link voltage ripple by compensating for low-frequency harmonic components in neutral-point currents. The converter’s dynamic voltage regulation performance has been improved, with a measured ripple reduction exceeding 80%. (2) Under fault conditions, the redundant fully-controlled devices are shared among faulty bridge arms across different phases, enabling reliable fault ride-through of multiple switch open-circuit faults without the output voltage magnitude. The proposed fault-tolerant 3L-HANPC topology demonstrates significant applicability in high-reliability scenarios such as photovoltaic power generation and electric drive systems. It effectively mitigates the risk of substantial economic losses and safety hazards caused by switching faults.
[1] 李锦, 党恩帅, 范雨顺, 等. 一种碳化硅与硅器件混合型三电平有源中点钳位零电压转换软开关变流器[J]. 电工技术学报, 2024, 39(8): 2496-2510. Li Jin, Dang Enshuai, Fan Yushun, et al.A hybrid three-level active-neutral-point-clamped zero-voltage transition soft-switching converter with silicon carbide and silicon devices[J]. Transactions of China Electrotechnical Society, 2024, 39(8): 2496-2510. [2] 刘伟志. 基于SiC器件的三电平ANPC牵引变流器损耗分析[J]. 电气传动, 2023, 53(2): 16-23. Liu Weizhi.Design and loss analysis of three-level ANPC topology based on SiC device in traction drive system[J]. Electric Drive, 2023, 53(2): 16-23. [3] 李锦, 焦娜娜, 黄敏超, 等. 不同PWM调制方式下器件混合型三电平变流器EMI特性研究[J]. 电源学报, 2025, 23(5): 306-315. Li jin, Jiao Nana, Huang Minchao, et al. Research on EMI characteristics of three-level converter with hybrid devices in different PWM modes[J]. Journal of Power Supply, 2025, 23(5): 306-315. [4] 许水清, 许晓凡, 何怡刚, 等. 基于自适应滑模观测器的中点钳位型三电平并网逆变器开关管和电流传感器故障诊断[J]. 电工技术学报, 2024, 39(13): 4066-4078. Xu Shuiqing, Xu Xiaofan, He Yigang, et al.A diagnosis method for power switch and current sensor faults in grid-connected three-level neutral-point clamped inverters based on adaptive sliding mode observer[J]. Transactions of China Electrotechnical Society, 2024, 39(13): 4066-4078. [5] 赵楠, 郑泽东, 刘建伟, 等. 级联H桥变换器IGBT开路故障分析与冗余方法研究[J]. 电工技术学报, 2023, 38(6): 1608-1619. Zhao Nan, Zheng Zedong, Liu Jianwei, et al.IGBT open-circuit fault analysis and fault-tolerant method for cascaded H-bridge converter[J]. Transactions of China Electrotechnical Society, 2023, 38(6): 1608-1619. [6] 翟道宇, 孙燕楠. 基于卷积神经网络和格拉姆角差场的四象限脉冲整流器故障诊断方法[J]. 电气技术, 2025, 26(1): 23-32. Zhai Daoyu, Sun Yannan.Fault diagnosis for four- quadrant pulse rectifiers based on convolutional neural network and Gramian angular difference field[J]. Electrical Engineering, 2025, 26(1): 23-32. [7] 陈超波, 代佳伟, 孙天誉, 等. 面向残差评价的中点钳位型逆变器开路故障诊断方法[J]. 电工技术学报, 2024, 39(21): 6877-6895. Chen Chaobo, Dai jiawei, Sun Tianyu, et al. NPC type inverter open circuit fault diagnosis method based on residual performance evaluation[J]. Transactions of China Electrotechnical Society, 2024, 39(21): 6877-6895. [8] 管硕, 马建军, 朱淼, 等. 计及二次侧开关开路故障的半有源桥变换器多模式容错运行策略[J]. 电工技术学报, 2024, 39(6): 1843-1858. Guan Shuo, Ma Jianjun, Zhu Miao, et al.Multi-mode fault-tolerant operation strategy of semi-dual active bridge converter considering open circuit fault of the secondary side switch[J]. Transactions of China Electrotechnical Society, 2024, 39(6): 1843-1858. [9] Choi U M, Blaabjerg F, Lee K B.Reliability improvement of a T-type three-level inverter with fault-tolerant control strategy[J]. IEEE Transactions on Power Electronics, 2015, 30(5): 2660-2673. [10] Lee J S, Choi U M, Lee K B.Comparison of tolerance controls for open-switch fault in a grid-connected T-type rectifier[J]. IEEE Transactions on Power Electronics, 2015, 30(10): 5810-5820. [11] Chen Jie, Zhang Chenghui, Chen Alian, et al.Fault- tolerant control strategies for T-type three-level inver- ters considering neutral-point voltage oscillations[J]. IEEE Transactions on Industrial Electronics, 2019, 66(4): 2837-2846. [12] Guan Bo, Liu Zhenhua.Hybrid modulation strategy with neutral point potential balance of T-type three- level converter under switch open-circuit fault[J]. IEEE Transactions on Industrial Electronics, 2022, 69(11): 10797-10806. [13] Azer P, Ouni S, Narimani M.A novel fault-tolerant technique for active-neutral-point-clamped inverter using carrier-based PWM[J]. IEEE Transactions on Industrial Electronics, 2020, 67(3): 1792-1803. [14] Halabi L M, Alsofyani I M, Lee K B.Multi open-/ short-circuit fault-tolerance using modified SVM technique for three-level HANPC converters[J]. IEEE Transactions on Power Electronics, 2021, 36(12): 13621-13633. [15] Chen Jie, Zhang Chenghui, Xing Xiangyang, et al.A fault-tolerant control strategy for T-type three-level rectifier with neutral point voltage balance and loss reduction[J]. IEEE Transactions on Power Electronics, 2020, 35(7): 7492-7505. [16] Wu Mingzhe, Pang Jupeng, Ma Zunmin, et al.A unified fault tolerant control and neutral-point voltage balance strategy for three-level T-type inverters under double signal PWM[J]. IEEE Transactions on Power Electronics, 2024, 39(11): 14204-14215. [17] Katebi R, He Jiangbiao, Weise N.An advanced three- level active neutral-point-clamped converter with improved fault-tolerant capabilities[J]. IEEE Transa- ctions on Power Electronics, 2018, 33(8): 6897-6909. [18] Wang Borong, Li Zhan, Bai Zhihong, et al.A redundant unit to form T-type three-level inverters tolerant of IGBT open-circuit faults in multiple legs[J]. IEEE Transactions on Power Electronics, 2020, 35(1): 924-939. [19] Do D T, Tran V T, Nguyen M K, et al.Fault tolerant control methods for three-level Boost T-type inver- ter[J]. IEEE Transactions on Industrial Electronics, 2023, 70(6): 5463-5473. [20] Do D T, Tran V T, Le H G, et al.Fault-tolerant methods for three-level Boost T-type inverter with capacitor voltage reduction[J]. IEEE Transactions on Industrial Electronics, 2024, 71(9): 10739-10749. [21] Deng Qingli, Ge Xinglai, Lin Chunxu, et al.An optimized SVPWM strategy for the postfault three- level NPC voltage source inverters[J]. IEEE Transa- ctions on Industry Applications, 2021, 57(6): 6182-6194. [22] Tang Yi, Blaabjerg F, Loh P C.Decoupling of fluctuating power in single-phase systems through a symmetrical half-bridge circuit[C]//2014 IEEE Applied Power Electronics Conference and Exposition-APEC 2014, Fort Worth, TX, USA, 2014: 96-102. [23] Zhang Li, Shi Donghan, Yang Tianbo, et al.Partial power processing for power decoupling network in three-phase three-leg four-wire three-level T-type inverter with reduced split DC-bus capacitance[J]. IEEE Transactions on Industrial Electronics, 2022, 69(4): 3643-3655. [24] Guo Feng, Yang Tao, Diab A M, et al.Hybrid active modulation strategy for three-level neutral-point- clamped converters in high-speed aerospace drives[J]. IEEE Transactions on Industrial Electronics, 2023, 70(4): 3449-3460. [25] Yan Qingzeng, Xiao Langtao, Chen Haoming, et al.An analytical discontinuous space-vector PWM for three-level inverters with unbalanced DC-link voltages[J]. IEEE Transactions on Power Electronics, 2022, 37(7): 7718-7728. [26] Li Xiaoyan, Xing Xiangyang, Zhang Chenghui, et al.Neutral-point voltage oscillation mitigation scheme for transformerless three-level PV inverter in LVRT operation with selective space vector modulation[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2022, 10(3): 2776-2789.
2026, Vol. 41 
